The invention relates to a method for purging the eroding zone during electroerosive countersinking, in which first raising/lowering movements of the tool electrode relative to the workpiece are performed in the dielectric.
The invention also relates to an apparatus for purging the eroding zone in an electroerosive countersinking installation with a raising/lowering device for bringing about first raising/lowering movements of the tool electrode relative to the workpiece in the dielectric.
Such methods and apparatuses are generally known in connection with electroerosive countersinking installations. The aforementioned raising/lowering movements have a pumping effect in the dielectric, e.g. an oil, which can be used for purging and in particular for cleaning the eroding zone.
The following procedure is normally adopted during countersinking erosion. On the basis of the actual erosion installation, e.g. the available purging device, the electrode used and the workpiece to be machined, as well as the sought working objective, e.g. the desired geometry, the desired surface quality, the eroding intensity, the small amount of wear, etc., on the basis of existing technological guidelines, the geometrical (.DELTA.R, .DELTA.B, .DELTA.Z, .DELTA.X, .DELTA.Y) and the method-specific (U, I, T, Q etc.) parameters, also called off-line parameters are determined, whereby the meanings are as follows:
.DELTA.R: radial advance step (e.g. for stepwise widening) PA2 .DELTA..beta.: angular increment for radial working movement PA2 .DELTA.Z: Z-axial increment PA2 .DELTA.X: X-axial increment PA2 .DELTA.Y: Y-axial increment PA2 U: no-load voltage PA2 I: current intensity PA2 T: pulse length PA2 Q: purging quantity
If the aforementioned off-line parameters have been carefully chosen, the erosion process can start. The erosion process can e.g. be characterized by pulse-specific, physical parameters, such as the igniting delay time t.sub.d, the short-circuit part t.sub.c, etc. These parameters can be influenced by the so-called on-line actions on the servosensitivity , the servoreference voltage in the gap, the eroding zone scavenging .DELTA.Q, the internal time .DELTA.}, etc.
The quality of an electroerosive countersinking process can be characterized by the process efficiency and the process stability. The process efficiency supplies information on the efficiency of the physical process, e.g. the no-load part and the short-circuit part. The process stability provides information on the dynamic behaviour of the machining, e.g. the spindle sleeve movement, etc.
The process efficiency and stability are reduced by any process problem. Unfortunately the erosion process is always accompanied by problems, which are caused by the process, or which are imparted to the latter from the outside.
Generally during an electrorosive countersinking process actions are necessary in order to guarantee its further performance, e.g. if an arc starts to form in the depth of the working or eroding zone. For such cases an electroerosion plant contains monitoring systems, called automatic anti-short-circuit systems. In a countersinking erosion installation these systems frequently lead to a raising/lowering movement or simply a return movement of the spindle sleeve in the case of a fault.
These raising/lowering movements, which are also called timer movements, are used for cleaning the working zone and therefore make the working process safe.
It is also known not only to perform these timer movements in the case of a short-circuit, but also on precautionary basis at regular intervals, so as to prevent short-circuits as far as this is possible. A certain action frequency can be given thereto by the machine operator, or in other words there is a specific time interval between two timer movements. This action frequency is generally dependent on the given off-line parameters, but also by the penetration depth of the tool electrode in the working zone. The height of stroke of the timer movements can also be predetermined.
However, the timer movements impair the process stability and sufficiency and in particular increase the working time.